1. Field of the Invention
The invention relates to a motor rotor which has segment magnets extending in the axial direction of a rotor yoke and respectively fixed to a plurality of magnet fixing sections formed on the lateral surface of the rotor yoke, and an electric power steering apparatus provided with a motor having the rotor as a motive power source.
2. Description of the Related Art
This type of rotor has a structure in which a plurality of grooves extending in the axial direction of a rotor yoke are formed on the lateral surface thereof, and segment magnets are fixed in each groove by being received therein. The segment magnets are sandwiched in the width direction by projections formed between adjacent grooves, and movement of the segment magnets in the width direction is restricted (see Japanese Patent Application Publication No. 2006-271057 (JP-A-2006-271057)).
However, as shown in the magnetic flux distribution diagram of FIG. 9, when a projection 2 is provided between segment magnets 1,1, although magnetic flux should inherently pass between the segment magnets 1 and the stator core 3 of the motor, magnetic flux extends in the form of a loop between the segment magnet 1 and the projection 2, resulting in the occurrence of so-called “magnetic leakage”. For example, the magnetic leakage is occurring on the right end of the segment magnets 1 in FIG. 9. In a rotor as described above, since projections are formed continuously extending between both ends of the rotor yoke in the axial direction, leakage of magnetism to the projections occurs over the entire axial direction of the rotor yoke, thereby resulting in the problem of exacerbation of motor characteristics. In addition, in an electric power steering apparatus assisted by a motor, it is necessary to improve motor characteristics since exacerbation of motor characteristics is transmitted to the hands and a driver feels poor steering feel.